Fe and Mn levels regulated by agricultural activities in alluvial groundwaters underneath a flooded paddy field

• Published in: Applied geochemistry Vol. 23; no. 1; pp. 44 - 57
• Main Authors: Kim, Kangjoo, Kim, Hyun-Jung, Choi, Byoung-Young, Kim, Seok-Hwi, Park, Ki-hoon, Park, Eungyu, Koh, Dong-Chan, Yun, Seong-Taek
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 2008; Elsevier
• Subjects: Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Exact sciences and technology; Hydrogeology; Hydrology. Hydrogeology; Pollution, environment geology; floods; mass balance; fertilization; ground water; point bars; concentration; shallow depth; samplers; infiltration; irrigation; aquifers; iron; reduction
• ISSN: 0883-2927; 1872-9134
• DOI: 10.1016/j.apgeochem.2007.09.004

Iron and Mn concentrations in fresh groundwaters of alluvial aquifers are generally high in reducing conditions reflecting low SO 4 concentrations. The mass balance and isotopic approaches of this study demonstrate that reduction of SO 4, supplied from agricultural activities such as fertilization and irrigation, is important in lowering Fe and Mn levels in alluvial groundwaters underneath a paddy field. This study was performed to investigate the processes regulating Fe and Mn levels in groundwaters of a point bar area, which has been intensively used for flood cultivation. Four multilevel-groundwater samplers were installed to examine the relationship between geology and the vertical changes in water chemistry. The results show that Fe and Mn levels are regulated by the presence of NO 3 at shallow depths and by SO 4 reduction at the greater depths. Isotopic and mass balance analyses revealed that NO 3 and SO 4 in groundwater are mostly supplied from the paddy field, suggesting that the Fe-and Mn-rich zone of the study area is confined by the agricultural activities. For this reason, the geologic conditions controlling the infiltration of agrochemicals are also important for the occurrence of Fe/Mn-rich groundwaters in the paddy field area.